139
Turns out all we may need to stop climate change is 139 billion gallons of super-duper white paint
(www.businessinsider.com)
This is a most excellent place for technology news and articles.
I mean it literally can't. You wouldn't build a giant one. Your built thousands. With material from the moon if you want them cheaper.
And then you park them in orbit. If you don't need them, set them to slant and let light pass. And so on